IRF-1 expression in normal human epidermal keratinocytes

The influence of hydration status on ion transport in the rabbit (Oryctolagus cuniculus) skin-An in vitro study

The preservation of physiological transport of ions and water content is particularly important for maintaining the skin barrier, touch and pain stimuli, as well as the initiation of skin regeneration processes, especially after treatments associated with breaking skin continuity and wound healing difficulties. The aim of the study was to assess changes in ion transport, measured as values of transepithelial electric resistance and potential difference in stationary conditions and during mechanical-chemical stimulations, depending on the hydration status of isolated rabbit skin specimens. The specimens were divided into five groups: control (n = 22), dehydrated in 10% NaCl (n = 30), rehydrated after dehydration (n = 26), dried at 37°C (n = 26), and rehydrated after drying (n = 25). Dehydrated tissue samples showed altered resistance compared to the control; this change was maintained regardless of rehydration. In the dehydrated samples, changes in the measured electric potential were also noted, which returned to values comparable with the control after rehydration. Dehydrated skin, regardless of the cause of dehydration, responds with changes in the transport of sodium and chloride ions and the altered cellular microenvironment. It could influence the perception of stimuli, particularly pain, and slow down the regeneration processes.

Human papillomavirus 16-encoded E7 protein inhibits IFN-γ-mediated MHC class I antigen presentation and CTL-induced lysis by blocking IRF-1 expression in mouse keratinocytes

Human papillomavirus 16 (HPV16) infection causes 50 % or more of cervical cancers in women. The HPV16 E7 oncogene is continuously expressed in infected epithelium with its oncogenicity linked to cervical cancer. The E7 protein is an ideal target in control of HPV infection through T-cell-mediated immunity. Using HPV16 E7-transgenic mouse keratinocytes (KCs-E7) to investigate T-cell-mediated immune responses, we have shown previously that HPV16-encoded E7 protein inhibits IFN-γ-mediated enhancement of MHC class I antigen processing and T-cell-induced target cell lysis. In this study, we found that HPV16 E7 suppresses IFN-γ-induced phosphorylation of STAT1((Tyr701)), leading to the blockade of interferon regulatory factor-1 (IRF-1) and transporter associated antigen processing subunit 1 (TAP-1) expression in KCs-E7. The results of a (51)Cr release assay demonstrated that IFN-γ-treated KCs-E7 escaped from CTL recognition because HPV16 E7 downregulated MHC class I antigen presentation on KCs. Restoration of IRF-1 expression in KCs-E7 overcame the inhibitory effect of E7 protein on IFN-γ-mediated CTL lysis and MHC class I antigen presentation on KCs. Our results suggest that HPV16 E7 interferes with the IFN-γ-mediated JAK1/JAK2/STAT1/IRF-1 signal transduction pathway and reduces the efficiency of peptide loading and MHC class I antigen presentation on KCs-E7. These results may reveal a new mechanism whereby HPV16 escapes from immune surveillance in vivo.

Characterization of retinoic acid-inducible gene-I (RIG-I) expression corresponding to viral infection and UVB in human keratinocytes

BACKGROUND

Retinoic acid-inducible gene-I (RIG-I) is a cytoplasmic protein that recognizes viral double-stranded RNA to induce the type I interferon (IFN) response. In human keratinocytes, RIG-I is induced by IFN-γ and tumor necrosis factor-α stimulation, and is abundantly expressed in psoriatic keratinocytes of the spinous and basal layers.

OBJECTIVE

This study investigated the effects of extraneous stimuli including viral infection and UVB exposure on RIG-I expression in human keratinocytes.

METHODS

Human skin keratinocytes (HaCaT cells) were stimulated by polyinosinic-polycytidylic acid (poly(I:C)), which mimics viral infection, and UVB exposure. We assessed the expression of RIG-I and IFN-regulatory factor (IRF)-1 in HaCaT cells by RT-PCR and Western blot analysis. Moreover, we investigated the effect of IRF-1 binding site of RIG-I gene promoter on the regulation of RIG-I expression by luciferase promoter assay and electrophoretic mobility shift assay.

RESULTS

Poly(I:C) induced RIG-I expression, while UVB inhibited basal RIG-I expression and the poly(I:C)-induced RIG-I overexpression in HaCaT cells. IRF-1, which binds to a regulatory element located on the RIG-I gene promoter, was required for both inductions of RIG-I expression. IRF-1 expression was enhanced three hours after the poly(I:C) stimulation, consistent with the RIG-I response to poly(I:C), and thereafter was suppressed. Moreover, UVB exposure promptly decreased IRF-1 expression, resulting in decreased IRF-1 protein binding to the RIG-I promoter, and consequently, decreased RIG-I expression.

CONCLUSION

Thus, suppression of RIG-I and IRF-1 expression caused by UVB exposure may partly explain the inhibition of skin-based immune responses, leading to viral infection and recrudescence.

Role of PKCdelta in IFN-gamma-inducible CIITA gene expression

The class II transactivator (CIITA) is a key regulatory factor for MHC class II expression. Here, we demonstrate that PKCdelta plays an important role in regulating IFN-gamma-inducible CIITA gene expression in macrophages. Inhibition of PKCdelta by either a PKCdelta inhibitor or a dominant negative (DN) mutant form of PKCdelta led to down-regulation of CIITA expression. The decrease in CIITA expression by PKCdelta inhibition was in part due to the reduced recruitment of serine 727-phosphorylated Stat1 and histone acetyltransferases to the CIITA promoter. As a result, IFN-gamma induced histone acetylation at the CIITA promoter is also compromised. However, inhibition of PKCdelta did not affect IRF-1 expression or IRF-1 binding to the CIITA promoter. Therefore, we report, for the first time, that PKCdelta is an essential signaling molecule to achieve the maximal expression of CIITA in response to IFN-gamma in macrophages. In addition, although IRF-1 is a key transcription factor to activate the IFN-gamma inducible CIITA promoter, the effect of PKCdelta on CIITA expression is mediated primarily by serine phosphorylation of Stat 1.

Transcriptional regulation of the 230-kDa bullous pemphigoid antigen gene expression by interferon regulatory factor 1 and interferon regulatory factor 2 in normal human epidermal keratinocytes

Interferon regulatory factors (IRFs) are a family of transcriptional factors induced by interferon-gamma (IFN-gamma). Recent studies have indicated that the deregulation of IRF system in keratinocytes is responsible, at least in part, for aberrant proliferation and the differentiation of the psoriatic epidermis. Previously, we reported that the expression of 230-kDa bullous pemphigoid antigen (BPAG1) gene, which is strictly restricted to basal keratinocytes, is transcriptionally suppressed by IFN-gamma, but the contribution of IRFs in such suppression is still unclear. In this study, we investigated the role of IRFs in the regulation of BPAG1 gene expression. Computer analysis identified IRF1 and IRF2 consensus sequences between -135 and -123 on BPAG1 promoter region. Transient transfection studies with BPAG1 promoter-luciferase reporter gene plasmids and IRF1 and IRF2 expression plasmids revealed that IRF1 and IRF2 directly down-regulated BPAG1 gene transcription in cultured normal human epidermal keratinocytes. Several sets of gel retardation assays with the BPAG1-IRF binding sequence as a probe indicated that IRF1 and IRF2 could bind to the BPAG1-IRF sequence, but some other protein(s), which was induced by IFN-gamma stimulation and possessed binding activity to IRF consensus sequence, showed preferential binding to the BPAG1-IRF sequence. Our results suggest that IFN-gamma-IRF system is involved in BPAG1 gene regulation in type-1 helper T-cell inflammatory skin conditions, such as psoriasis vulgaris.

Expression of double-stranded RNA-activated protein kinase in keratinocytes and keratinocytic neoplasia

Double-stranded RNA-activated protein kinase (PKR) is a interferon-induced protein initially known for its inhibitory effects on cellular and viral protein synthesis. In recent studies, PKR has been shown to be an important participant in a broad array of cellular processes, including signal transduction, differentiation, apoptosis, cell growth, and tumorigenesis. The expression of PKR in normal human keratinocytes (NHEK) was examined, and its expression in several skin lesions was compared immunohistochemically with that of proliferating cell nuclear antigen (PCNA). Expression of PKR mRNA was detected in NHEK without IFNgamma treatment; the level of PKR mRNA increased with IFNgamma treatment for two hours. Immunoblot analysis revealed that the monoclonal anti-PKR antibody reacted specifically with a 68kDa PKR protein in extracts from NHEK. Immunohistochemistry revealed that PKR protein was expressed in normal epidermis and mucosa. PKR expression was not restricted only to suprabasal cells but was also observed in basal cells positive for PCNA. In psoriatic plaques, PKR expression was lower in basal and parabasal keratinocytes and comparable in suprabasal keratinocytes to the levels in normal skin. PKR was partially detected in atypical cells in non-invasive keratinocytic neoplasia but was completely absent from undifferentiated tumor cells of squamous cell carcinoma. The present study demonstrated that PKR protein is constitutively expressed in epidermal and epithelial keratinocytes of normal skin and mucosa and indicated that a loss of PKR is not associated with the malignant transformation itself but with the increased cell proliferative activity and the altered differentiation of keratinocytes.

Decreased growth inhibitory responses of squamous carcinoma cells to interferon-gamma involve failure to recruit cki proteins into cdk2 complexes

Interferon-gamma induces an irreversible growth arrest and squamous differentiation in normal human epidermal keratinocytes. We present for the first time a careful biochemical analysis of the cell-cycle-related events that occur during interferon-gamma treatment of normal human epidermal keratinocytes. The interferon-gamma-induced irreversible growth arrest state is characterized by inhibition of cyclin-dependent kinases, prevention of Rb and p130 (Rb2) phosphorylation, and increases in p27(Kip1), p16(Ink4a), and p130 proteins, together with a transient increase in p21(Waf1/Cip1). Cells derived from squamous cell carcinomas are less responsive to interferon-gamma and do not terminally differentiate. We exploited these differences in response to interferon-gamma in order to identify the particular molecular defects in cell cycle control that promote carcinogenesis in squamous epithelia. In several squamous cell carcinoma cell lines as well as in interferon-gamma-insensitive HaCaT cells, interferon gamma was unable to significantly induce levels of p130 and/or p16 protein. In addition, p21 association with cdk2 complexes was undetectable in either the absence or the presence of interferon-gamma and, unlike normal human epidermal keratinocytes, p27 association with cdk2 did not increase with interferon-gamma treatment. These multiple defects appear to be intrinsic to the mechanisms of cell cycle regulation rather than due to defects in the interferon-gamma signaling pathway, as induction of several interferon-gamma-responsive genes including Stat 1, IRF-1, and p21 itself was normal. Interestingly, exogenous expression of p21 protein in the squamous cell carcinoma cell lines by adenovirus carrying wildtype p53 or p21 cDNA cooperated with interferon-gamma to produce a greater inhibition of growth than either agent alone, even though p21 protein could barely be detected in cdk2 complexes. We conclude that squamous cell carcinoma cells have intrinsic defects in their ability to regulate cdk-cki complexes in response to differentiation signals.